Explain the following.
a. Hydrated barium peroxide is used in the preparation of `H_(2)O_(2)` instead of anhydrous barium peroxide.
b. Phosphoric acid is preferred to sulphuric acid in the preparation of `H_(2)O_(2)` from barium peroxide..

Explanation

a. If anhydrous barrium peroxide is used in the preparation of `H_(2)O_(2),` the `BaSO_(4)` formed during the reaction forms an insoluble protective coating on the surface of solid barium peroxide.
`BaO_(2(s))+H_(2)SO_(4(aq))toBaSO_(4(s))+H_(2)O_(2(aq))`
This presents further action of the acid and ultimately the reaction stops. if however, hydrated barium peroxide (in the form of thin paset) is used, the water of crystallisation does not allow `BaSO_(4)` to deposit on the surface of `BaO_(2)` and the reaction goes to completion.
b. the aqueous solution of `H_(2)O_(2)` prepared by the action of dil `H_(2)O_(2)` on hydrated `BaO_(2)` has impurities of heavey metals ions such as a `Ba^(2+),Pb^(2+)` etc. which catalyse the decomposition of `H_(2)O_(2)`. hence, the `H_(2)O_(2)` does not have good keeping quality. if phospheric acid, `H_(3)PO_(4)`, is used, the impurities of heavy metals are percipitated as insoluble phosphates. As a results, the resulting solution of `H_(2)O_(2)` has good keeping qualities.
c. Conc `H_(2)SO_(4)` reacts with zinc to form `SO_(2)` rather than `H_(2)`.
`Zn+underset("conc")(H_(2)SO_(4))toZnSO_(4)+SO_(2)+2H_(2)`
d. Dihydrogen, `H_(2)` is less reactive and hence it does not reduce acidified `FeCl_(3)` solution. however, when zinc is added to acidified `FeCl_(3)` solution, nascent hydrogen thus produced is associated with more energy. consequently, it is more reactive and hence acidified `FeCl_(3)` solution.
`FeCl_(3)+H_(2)toNo reaction`
`Zn+H_(2)SO_(4)toZnSO_(4)+2[H]`
`2[H]+underset("Yellow")(FeCl_(3))tounderset("Green")(FeCl_(2))+2HCl`